The present invention is directed to a method of manufacturing a polymer/clay slurry-filled sheet material, and particularly to a continuous method of manufacturing the polymer/clay-filled sheet material including a step of embedding a high viscosity aqueous polymerization solution, containing a polymerizable monomer and a water swellable clay, in the form of a slurry, into a liquid-absorbent or liquid adsorbent substrate that contains a polymerization catalyst and/or a polymerization initiator for subsequent polymerization of the monomer, without premature polymerization of the monomer. In the preferred embodiment, the monomer is polymerized, in-situ, at a temperature sufficient to vaporize the slurry water, e.g., at least 100xc2x0 C. at atmospheric pressure.
Published PCT application WO 00/72958 A1 (""958) describes a porous substrate, such as a geotextile liner, containing a polymer, such as polyacrylamide and/or a polyacrylic acid, that is partially neutralized (e.g., polyacrylic acid and sodium polyacrylate), and preferably also clay. The polymer is formed for the most part, in situ, while the monomer is embedded into the geotextile, together with the clay, to provide a hydraulic barrier that has excellent, low hydraulic conductivity and has a significantly lower weight of active barrier material than the weight of active barrier material contained in geosynthetic liners in existence at the time of the ""958 invention. Further, as disclosed in the ""958 publication, there may be some synergy in the combination of a polymerizable monomer, such as acrylic acid, and clay by virtue of intercalation of the monomer between the clay platelets to form an intercalate during the mixing of the monomer and clay to form a slurry for embedment into a geotextile and/or during the embedding of the slurry into the geotextile.
It has been found that the manufacture of an article, in accordance with WO 00/72958 results in a product that contains a substantial percentage of water, making it more difficult to apply the product over a surface to be protected against water penetration, and making shipping of the product more expensive, thereby detracting from the low weight advantage and cost savings attributed to having less active barrier material in the geotextile. Further, in accordance with WO 00/72958 A1, an aqueous polymerization solution, a polymerization catalyst, and a cross-linker are premixed and embedded into the porous substrate simultaneously during continuous manufacture. It has been found that only small batches of the polymerizable monomer can be prepared or the polymerizable monomer will begin to polymerize prior to embedding the polymerization solution into the porous substrate resulting in lower hydraulic barrier properties and decreased retention of solids.
In accordance with the method of manufacture described herein, it has been found that by applying a polymerization catalyst or polymerization initiator directly to a liquid-absorbent or liquid adsorbent (hereinafter collectively referred to as xe2x80x9cliquid-sorbentxe2x80x9d) substrate, preferably a porous geotextile in sheet material form, to form a polymerization-initiating substrate or sheet material, a slurry of water, clay, and a polymerizable monomer that is subsequently embedded in the polymerization-initiating substrate will be completely contacted by the polymerization catalyst or polymerization initiator for complete polymerization of the embedded monomer to form embedded polymer solids, without the monomer partially polymerizing before contacting the substrate. It has been found that complete polymerization of the monomer while in contact with the polymerization-initiating substrate achieves best results in retention of embedded and interlocked polymer solids. Preferably only the polymerization catalyst or polymerization initiator, and optionally a cross-linker for the monomer, and/or a polymer neutralizing agent, together with any carrier, such as water or an organic solvent, are applied to the liquid-sorbent substrate prior to embedding the monomer into the substrate.
In accordance with the method disclosed herein, an aqueous polymerization solution containing a polymerizable monomer and clay that is void of polymerization catalyst or polymerization initiator can be mixed in large batches, and the batches will not polymerize prematurely, prior to being embedded into the liquid-sorbent substrate. Further, by providing a liquid-monomer absorbent or liquid monomer adsorbent substrate containing the polymerization catalyst or polymerization initiator, an effective polymerization solution containing a polymerizable monomer and clay, in the form of a monomer clay slurry, can be conveyed to the substrate with a minimum amount of carrier, such as water and/or organic solvent, such that the monomer/clay-containing polymerization solution is easily embedded into the catalyst-containing substrate, to minimize drying time and solvent expense.
Accordingly, one aspect of the articles and methods described herein is to provide a method of manufacturing a sheet material containing an embedded polymer that is polymerized, in-situ, essentially only while in contact with a liquid-sorbent polymerization initiating substrate by embedding a polymerizable monomer/clay slurry, that is void of polymerization catalyst and polymerization initiator, into a liquid-sorbent polymerization-initiating substrate for contact with the polymerization catalyst and/or polymerization initiator and subsequent contact with the polymerizable monomer for polymerization, in-situ. The embedded monomer is polymerized only while in contact with the sheet material that has been pre-loaded with polymerization catalyst and/or polymerization initiator for the polymerizable monomer. In accordance with the methods disclosed herein, the preliminary step of first loading the sheet material, or the sheet material components, e.g., fibers used to make the sheet material, with a polymerization catalyst or polymerization initiator prior to contacting the sheet material with the polymerizable monomer/clay slurry, provides tenacious interlocking of the polymer and clay within the substrate. Further, large batches of the monomer/clay slurry that are void of polymerization catalyst and/or a polymerization initiator for the polymerizable monomer can be prepared without premature polymerization of the monomer.
Another aspect of the methods and articles disclosed herein is to provide a method of manufacturing a hydraulic barrier in sheet material form containing a liquid-sorbent polymer and a liquid absorbent clay. The polymer and clay are structurally reinforced with a sheet material, particularly a fibrous sheet material, such as a geotextile, woven or non-woven, loaded with a liquid-sorbent polymer and a water-absorbent clay in a weight ratio of polymer:clay in the range of 1:19 to 19:1, preferably in the range of 1:1 to 1:5, more preferably in the range of 1:1 to 1:4, most preferably in the range of 1:2 to 1:4. The geotextile, or the fibers used to make the geotextile, are first loaded with a polymerization catalyst or a polymerization initiator, and thereafter a viscous slurry containing one or more polymerizable monomers and a water-absorbent clay is loaded into the liquid-sorbent polymerization initiating substrate such that monomer polymerization does not begin until the monomer/clay slurry contacts the polymerization initiating substrate, such that the monomer is essentially completely polymerized, in-situ, for tenacious adherence of the polymer and clay to the sheet material. In the preferred embodiment, the polymer is sufficiently cross-linked, e.g., for water insolubility and water absorbency. Sufficient cross-linking is achieved with at least about 0.1% by weight, preferably at least about 0.1%, cross-linker, based on the weight of polymerizable monomer. It is preferred to add the monomer cross-linking agent in a ratio of cross-linking agent to monomer in the range of about 1:100 to 1:1000; more preferably in the range of about 1:250 to 1:750; most preferably in the range of about 1:400 to 1:600.
In the preferred embodiment, the liquid-sorbent substrate is embedded with about 20% to about 50% by weight monomer, and about 50% to about 80% clay, based on the total weight of monomer and clay in the monomer/clay slurry. Preferably, the polymerization solution has a weight ratio of clay to water in the range of about 2:8 to 8:2, more preferably 3:2 to 2:3, most preferably about 1:1. The monomer is polymerized, with water evaporation, until the polymer/clay-containing substrate contains less than about 15% by weight water, preferably less than about 12% by weight water.
The above and other aspects and advantages of the manufacturing method and articles disclosed herein will become more apparent from the following detailed description taken in conjunction with the drawings.